Is it worth filing for the I-765, Application for Employment Authorization form, even though I don't plan to work until I have received my Green Card? Or is it something that HAS to be filed with the AOS?

I-765 is OPTIONAL.

You can file it WITH or After filing your I-485. If you file it after filing the I-485, you will need to attach a copy of I-485 NOA1 letter to prove no fee is required.

When We filed for AOS we decided to include EAD just in case it took a long time for GC to be processed since the EAD card usually is received within3-4 months from filing. GC can take 5-8 months.

We realised we probably could have waited and saved the money, but we did get the ead card in about 3 months, so my wife was able to get her SS# , Drivers liscense and open a joint account. All this was useful to present at the interviewas support documentation
with her Drivers liscense she was added onto my Auto insurance
we opened a Joint Bank Account.
& with her ss# if she needed to work she could have.

If the beneficiary won't need to be working or driving withing 6 months from filing AOS I say save the money & wait for GC. it is optional but not all that useful unless your case is complicated and may take longer than 6 months

There's no money to be saved by not filing for EAD together with AOS, the fee is still $1,010. It also includes Advance Parole. Besides working, the alien should be able to get a driver's license and SSN with the EAD card.

K-1 can get SSN within 76 days of entry, but yes in most states having EAD helps with getting a driver's license, and other things.
EAD also makes a useful ID for the time before getting green-card.

It worth getting, you never know what kind of delay you may face with the green card. Somebody here just got his after 918 days of waiting. That's 2.5 years. You never know.

It's free (included in fee), so why not do it... The form is only one page and you just need to provide a couple supporting docs, not many. It's all in the instructions and GUIDES on this site.